1 use crate::infer::{InferCtxt, TyCtxtInferExt};
2 use crate::traits::ObligationCause;
3 use crate::traits::{self, TraitEngine};
5 use rustc_data_structures::fx::FxHashSet;
7 use rustc_hir::lang_items::LangItem;
8 use rustc_middle::ty::query::Providers;
9 use rustc_middle::ty::{self, AdtDef, Ty, TyCtxt, TypeFoldable, TypeVisitor};
11 use std::ops::ControlFlow;
14 pub enum NonStructuralMatchTy<'tcx> {
25 /// This method traverses the structure of `ty`, trying to find an
26 /// instance of an ADT (i.e. struct or enum) that doesn't implement
27 /// the structural-match traits, or a generic type parameter
28 /// (which cannot be determined to be structural-match).
30 /// The "structure of a type" includes all components that would be
31 /// considered when doing a pattern match on a constant of that
34 /// * This means this method descends into fields of structs/enums,
35 /// and also descends into the inner type `T` of `&T` and `&mut T`
37 /// * The traversal doesn't dereference unsafe pointers (`*const T`,
38 /// `*mut T`), and it does not visit the type arguments of an
39 /// instantiated generic like `PhantomData<T>`.
41 /// The reason we do this search is Rust currently require all ADTs
42 /// reachable from a constant's type to implement the
43 /// structural-match traits, which essentially say that
44 /// the implementation of `PartialEq::eq` behaves *equivalently* to a
45 /// comparison against the unfolded structure.
47 /// For more background on why Rust has this requirement, and issues
48 /// that arose when the requirement was not enforced completely, see
49 /// Rust RFC 1445, rust-lang/rust#61188, and rust-lang/rust#62307.
50 pub fn search_for_structural_match_violation<'tcx>(
55 ) -> Option<NonStructuralMatchTy<'tcx>> {
56 // FIXME: we should instead pass in an `infcx` from the outside.
57 tcx.infer_ctxt().enter(|infcx| {
58 ty.visit_with(&mut Search { infcx, span, seen: FxHashSet::default() }).break_value()
62 /// This method returns true if and only if `adt_ty` itself has been marked as
63 /// eligible for structural-match: namely, if it implements both
64 /// `StructuralPartialEq` and `StructuralEq` (which are respectively injected by
65 /// `#[derive(PartialEq)]` and `#[derive(Eq)]`).
67 /// Note that this does *not* recursively check if the substructure of `adt_ty`
68 /// implements the traits.
69 fn type_marked_structural<'tcx>(
70 infcx: &InferCtxt<'_, 'tcx>,
72 cause: ObligationCause<'tcx>,
74 let mut fulfillment_cx = traits::FulfillmentContext::new();
75 // require `#[derive(PartialEq)]`
76 let structural_peq_def_id =
77 infcx.tcx.require_lang_item(LangItem::StructuralPeq, Some(cause.span));
78 fulfillment_cx.register_bound(
80 ty::ParamEnv::empty(),
82 structural_peq_def_id,
85 // for now, require `#[derive(Eq)]`. (Doing so is a hack to work around
86 // the type `for<'a> fn(&'a ())` failing to implement `Eq` itself.)
87 let structural_teq_def_id =
88 infcx.tcx.require_lang_item(LangItem::StructuralTeq, Some(cause.span));
89 fulfillment_cx.register_bound(
91 ty::ParamEnv::empty(),
93 structural_teq_def_id,
97 // We deliberately skip *reporting* fulfillment errors (via
98 // `report_fulfillment_errors`), for two reasons:
100 // 1. The error messages would mention `std::marker::StructuralPartialEq`
101 // (a trait which is solely meant as an implementation detail
104 // 2. We are sometimes doing future-incompatibility lints for
105 // now, so we do not want unconditional errors here.
106 fulfillment_cx.select_all_or_error(infcx).is_empty()
109 /// This implements the traversal over the structure of a given type to try to
110 /// find instances of ADTs (specifically structs or enums) that do not implement
111 /// the structural-match traits (`StructuralPartialEq` and `StructuralEq`).
112 struct Search<'a, 'tcx> {
115 infcx: InferCtxt<'a, 'tcx>,
117 /// Tracks ADTs previously encountered during search, so that
118 /// we will not recur on them again.
119 seen: FxHashSet<hir::def_id::DefId>,
122 impl<'a, 'tcx> Search<'a, 'tcx> {
123 fn tcx(&self) -> TyCtxt<'tcx> {
127 fn type_marked_structural(&self, adt_ty: Ty<'tcx>) -> bool {
128 adt_ty.is_structural_eq_shallow(self.tcx())
132 impl<'a, 'tcx> TypeVisitor<'tcx> for Search<'a, 'tcx> {
133 type BreakTy = NonStructuralMatchTy<'tcx>;
135 fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
136 debug!("Search visiting ty: {:?}", ty);
138 let (adt_def, substs) = match *ty.kind() {
139 ty::Adt(adt_def, substs) => (adt_def, substs),
141 return ControlFlow::Break(NonStructuralMatchTy::Param);
144 return ControlFlow::Break(NonStructuralMatchTy::Dynamic);
147 return ControlFlow::Break(NonStructuralMatchTy::Foreign);
150 return ControlFlow::Break(NonStructuralMatchTy::Opaque);
152 ty::Projection(..) => {
153 return ControlFlow::Break(NonStructuralMatchTy::Projection);
156 return ControlFlow::Break(NonStructuralMatchTy::Closure);
158 ty::Generator(..) | ty::GeneratorWitness(..) => {
159 return ControlFlow::Break(NonStructuralMatchTy::Generator);
162 // structural-match ignores substructure of
163 // `*const _`/`*mut _`, so skip `super_visit_with`.
165 // For example, if you have:
167 // struct NonStructural;
168 // #[derive(PartialEq, Eq)]
169 // struct T(*const NonStructural);
170 // const C: T = T(std::ptr::null());
173 // Even though `NonStructural` does not implement `PartialEq`,
174 // structural equality on `T` does not recur into the raw
175 // pointer. Therefore, one can still use `C` in a pattern.
176 return ControlFlow::CONTINUE;
178 ty::FnDef(..) | ty::FnPtr(..) => {
179 // Types of formals and return in `fn(_) -> _` are also irrelevant;
180 // so we do not recur into them via `super_visit_with`
181 return ControlFlow::CONTINUE;
184 if { n.try_eval_usize(self.tcx(), ty::ParamEnv::reveal_all()) == Some(0) } =>
186 // rust-lang/rust#62336: ignore type of contents
188 return ControlFlow::CONTINUE;
190 ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str | ty::Never => {
191 // These primitive types are always structural match.
193 // `Never` is kind of special here, but as it is not inhabitable, this should be fine.
194 return ControlFlow::CONTINUE;
197 ty::Array(..) | ty::Slice(_) | ty::Ref(..) | ty::Tuple(..) => {
198 // First check all contained types and then tell the caller to continue searching.
199 return ty.super_visit_with(self);
201 ty::Infer(_) | ty::Placeholder(_) | ty::Bound(..) => {
202 bug!("unexpected type during structural-match checking: {:?}", ty);
205 self.tcx().sess.delay_span_bug(self.span, "ty::Error in structural-match check");
206 // We still want to check other types after encountering an error,
207 // as this may still emit relevant errors.
208 return ControlFlow::CONTINUE;
212 if !self.seen.insert(adt_def.did) {
213 debug!("Search already seen adt_def: {:?}", adt_def);
214 return ControlFlow::CONTINUE;
217 if !self.type_marked_structural(ty) {
218 debug!("Search found ty: {:?}", ty);
219 return ControlFlow::Break(NonStructuralMatchTy::Adt(&adt_def));
222 // structural-match does not care about the
223 // instantiation of the generics in an ADT (it
224 // instead looks directly at its fields outside
225 // this match), so we skip super_visit_with.
227 // (Must not recur on substs for `PhantomData<T>` cf
228 // rust-lang/rust#55028 and rust-lang/rust#55837; but also
229 // want to skip substs when only uses of generic are
230 // behind unsafe pointers `*const T`/`*mut T`.)
232 // even though we skip super_visit_with, we must recur on
234 let tcx = self.tcx();
235 adt_def.all_fields().map(|field| field.ty(tcx, substs)).try_for_each(|field_ty| {
236 let ty = self.tcx().normalize_erasing_regions(ty::ParamEnv::empty(), field_ty);
237 debug!("structural-match ADT: field_ty={:?}, ty={:?}", field_ty, ty);
243 pub fn provide(providers: &mut Providers) {
244 providers.has_structural_eq_impls = |tcx, ty| {
245 tcx.infer_ctxt().enter(|infcx| {
246 let cause = ObligationCause::dummy();
247 type_marked_structural(&infcx, ty, cause)